In arriving at a diagnosis a medical radiologist typically relies to a large extent, often entirely, on a visual study of silver images in photographic films. Image inspection usually occurs with the film mounted on a light box, a white, translucent illumination source. To facilitate an accurate diagnosis a number of varied images are usually mounted and studied together.
As employed herein the term "diagnostic photographic film" is employed to encompass the photographic films acceptable for producing the images studied for diagnosis. Acceptability depends not only on the quality of the image, but also on the rapidity of processing to render the image visually accessible.
Initially, silver halide photographic elements were exposed to X-radiation alone to produce viewable silver images. Because X-radiation is highly energetic, a large portion of the exposing X-radiation passes through a silver halide photographic element unabsorbed. Two strategies were developed to increase X-radiation absorption. First, silver halide emulsion layer units were coated on opposite sides of a film support, resulting in two superimposed silver images having the appearance of a single image of higher contrast. Second, intensifying screens were developed containing phosphors capable of absorbing X-radiation more efficiently than silver halide and promptly fluorescing to expose the silver halide with emitted longer wavelength light. In this arrangement the silver halide emulsion layer units are exposed to both X-radiation and emitted light, although the emitted light is primarily responsible for the image formed.
Since the patient being examined cannot be released until successful recording of the set of images needed for diagnosis has been confirmed, diagnostic photographic films have been constructed to provide a rapid-access imaging capability. The commonly accepted rapid-access standard is for processing to be completed in 90 seconds or less.
Dickerson et al U.S. Pat. No. 4,900,652 illustrates a diagnostic photographic film that provides a combination of low patient X-radiation dosage, high image quality and rapid-access processing typical of the highest standards of performance.
Although traditionally diagnostic photographic elements have themselves been exposed to X-radiation image patterns, even when longer wavelengths of light were primarily relied upon for latent image formation, alternatives are now becoming available to the radiologist for capturing the X-radiation image. For example, the X-radiation image can be captured in a storage phosphor screen. By subsequently scanning the exposed storage phosphor screen with stimulating radiation, an emission profile can be read out and sent to a computer for storage. An illustration of this imaging approach is provided by Luckey U.S. Pat. No. Re. 31,847 and DeBoer et al U.S. Pat. No. 4,733,090.
To provide the radiologist with a viewable image that can be studied in the same way as more traditionally captured images, the computer stored image information can be used as recorded or with computer enhancement to expose a diagnostic photographic film, usually using a modulated laser beam as an exposure source. After exposure the diagnostic photographic film is run through the same rapid-access processing cycle used for processing diagnostic photographic films directly exposed to X-radiation. It is important to note that the radiologist, for efficiency of effort, uses a single rapid-access processing route and, for accuracy of diagnosis, arrives at comparable viewable silver images in the diagnostic photographic films, even though the images are derived from alternative exposure routes.
One of the difficulties encountered by radiologists in studying images in diagnostic photographic films is surface glare (measured in terms of surface gloss). For example, specular reflection of room lights or adjacent light box panels can make accurate viewing of maximum density image areas impossible from a particular viewing position. Dimming other sources of illumination in the viewing room, shifting position and accepting a certain level of eye strain are the penalties involved. For a skilled diagnostician, surface glare is an obstacle to accurate diagnoses and a major source of fatigue.
The most closely relevant prior art diagnostic photographic film to the subject matter of this invention is commercially sold under the trademark Kodak Ektascan HN Film. In this diagnostic photographic film an interlayer is positioned between a silver halide emulsion layer unit and a gelatin overcoat. The interlayer contains a sensitized spherical grain silver halide emulsion with a silver coverage of 32 percent, based on total silver in the emulsion layer unit and interlayer. As originally introduced the film contained half this level (16 percent) of silver in the interlayer, but, as shown below, at this level the silver was relatively ineffective in reducing surface glare. The current diagnostic photographic film still exhibits significant surface glare, allowing bright, sharp specular reflections of fluorescent room lights to be viewed in maximum density areas of the processed film.
In addition to allowing a high level of surface glare to persist, a further disadvantage of the interlayer approach was that a relatively high proportion of additional silver was required in the interlayer to achieve modest glare reductions.
Of interest in connection with certain preferred forms of the invention, Plakonov U.S. Pat. No. 3,589,908 discloses to be useful in silver halide emulsions to increase speed and contrast a binder consisting of a combination of gelatin, a carboxymethylated protein, and at least one other hydrophilic colloid selected from the group consisting of polyacrylamide, polysaccharides, and poly-N-vinyl pyrrolidone.